Precipitation-hardening nonmagneticferrous alloys



Dec. 23, 1958 J. J. HEGER ETAL v 2,865,740

PRECIPITATION-HARDENING NONMAGNETIC-FERROUS ALLOYS Filed June 23, 1954 5 Sheets-Sheet 2 INVENTORS. JAMES J. HE CE I? JOHN M. H0065 and RAYMOND SMITH,

their Affo rney.

AND 0.40 TO 0.52 PERCENT I/A/VAO/UM STEEL EFFECT OF ALUMINUM //V A 0.34 TO 0.45 PERCENT CARBON m E Q n 000000000000000 6 2 6 QwwMMQwWQMZwm M Dec. 23, 1958 J. J. HEGER ETAL 2,865,749

PRECIPITATION-HARDENING NONMAGNETIC-FERROUS ALLOYS Filed June 23, 1954 5 Sheets-Sheet 5 HARD/VESS CHROM/UM "/a) EFFECT OF CHROM/UM IN A 0.40 PERCENT VA/VAD/UM AND M/ A 0.75 T0 /.0 PERCENT VA/VAD/UM STEEL 1/v VEN TORS.

JAMES J. HEGER, JOHN M. HODGE and RAYMOND SMITH,

their Afro/nay.

Dec. 23, 1958 J. J. HEGER ETAL 2,865,740

PRECIPITATION-HARDENING NONMAGNETIC-FERROUS ALLOYS Filed June 23, 1954 5 Sheets- Sheet 4 l-lA/PDNESS (0 PH) VANAD/UM "/a EFFECT OF l/ANAD/UM //V A 5.0 PERCENT CHROMIUM AND 0.40 7'0 0.50 PERCENT CARBON STEEL INVENTORS.

JAMES J. HEGER, JOHN M. H00 65 and mama/v0 SMM'H,

their Attorney.

Dec. 23, 1958 J. J. HEGER ETAL ,8

PRECIPITATION-HARDENING NONMAGNETICP-FERROUS ALLOYS Filed June 25, 1954 5 Sheets-Sheet 5 HARDNESS (DP/1) CARBON "/o) EFFECT OF CARBON /NA 5.0 PERCENT CHROM/UM AND /.0 PERCENT VANAD/UM STEEL JAMES .1. HEGER, uomv M. H0065 and RAYMOND SMITH,

the/r Attorney.

States Patent O PRECIPITATION-HARDENIN G NONMAGNETIC- FERROUS ALLOYS 'James J. Heger, Bridgeville, and John M. Hodge and Raymond Smith, Pittsburgh, Pa., assignors to United States Steel Corporation, a corporation of New Jersey Application June 23, 1954, Serial No. 438,816

9 Claims. (Cl. 75-123) This invention relates to austenitic ferrous alloys that can be hardened by precipitation-hardening heat treatments and precipitation-hardened articles formed therefrom.

There are numerous applications for austenitic steels that may beprecipitationor age-hardened whereby the necessity for cold working to achieve hardening may be avoided. While the use of phosphorus, titanium and other elements to achieve age-hardening in austenitic alloys of the high chromium type has been suggested, such ingredients have certain undesirable characteristics which render the'alloyeither unsuitable for many applications "or have an adverse effect on the hot working qualities thereof. Thehigh chromium stainless type austenitic alloys 'are widely used for high temperature applications due to their oxidation resistance and in many other instances where resistance to corrosion is a factor. There is however also a demand for austenitic, precipitation-hardenable alloys which contain either no chromium or relatively small amounts thereof. One particular use for the latter is retainer rings for large electrical generators. In order that such generators be not too massive, the steels used in their construction must have high strength and 'also must be nonmagnetic to prevent overheating-by eddy currents. Obviously, cold work is unsuitable for hardening such articles. I

It is accordingly an object of this invention to provide 2 age-hardenable, austenitic steels which have unimpaired working properties and no harmful inclusions therein.

" It is a further object of this invention to provide chromium containing austenitic steels which are age-hardenable.

It is another object of the present invention to provide low-nickel, manganese-nickel austenitic steels which are age-hardenable and also possess good hot and cold working qualities.

The foregoing and further objects will become apparent from the following specification when readin conjunction with the' attached drawings wherein Figures 1 through 5 are graphs, the ordinates of which show the (DPH) hardness values of steels containing the varying amounts "of alloying elements shown on the abscissasl. The broken horizontal line in each figure indicates the nominal annealed hardness of the steel.

We have discovered that the objects of this invention can be achieved by properly adjusting the elements carbon and vanadium in such austenitic steels and, if further age-hardening effects are desired, by the addition of aluminum thereto within certain critical amounts. Provided these elements are added within the ranges hereinafter disclosed, the steel can then be age-hardened by first heating it to a temperature high enough to dissolve the vanadium carbides, which form in the steels of our invention, and place such carbides in solution, cooling so as to retain the vanadium and carbon in solution and then reheating to a temperature above room temperature and below the temperature at which the vanadium carbides markedly increases the strength and hardness of the material.

In our steels the austenitic structure is preferably produced by suitable combinations of the elements manganese and nickel. Manganese may be present in amounts up to 16%; higher amounts could possibly be used so far as this invention is concerned except for steel melting difliculties which are associated with such higher amounts. Nickel may be present in amounts up to about 12%; high amounts are uneconomical. While the austenitic structure may be produced by additions of manganese alone or by additions of nickel alone, we have preferred to use combinations of manganese and nickel in which the nickel content is as low as possible for economical reasons. A small nickel content of the order of 2 to 4% is ordinarily preferred to enhance the hot working qualities.

In preparing our steels, at least 25% carbon is required. Considerably higher amounts of this element may be used, however it should not exceed about 1% as forging difiiculties are encountered above this amount. Vanadium should be above about 30%, preferably above .40% and may be present up to about 3%, the upper limit being dictated largely by economic reasons.

We have also discovered that certain additions of the elements chromium and molybdenum may be made to our steels for their normal effect on the corrosion or oxidation resistance of the steel without adversely affecting the precipitation hardening characteristics thereof and within certain limits a beneficial effect can be obtained. Aluminum can be added to further enhance the hardening effects.

Other elements such as phosphorus, silicon and sulphur may be present within ordinary commercial limits, i. e., .04% maximum phosphorus, .035% maximum sulphur and 1.0% maximum silicon. Other elementsmay be "present in residual amounts, the balance of the alloy scope of our invention are shown in the following Table I:

In" this table; we have listed the hardness after aging of a series of austenitic manganese-nickel steels having various amounts of carbon and vanadium. As will be noted, steel No. l which contains carbon but which does not contain vanadium will not age-harden, whereas the steels which contain over .30% vanadium and over .25% carbon undergo a considerable increase in hardness to above 230 DPH upon heating for 64 hours at 1200 F. This increase in hardness that occurs on heating is related to the amount of vanadium and the amount of carbon that are present in the steel, a certain minimum of each being required if a definite degree of hardening is to be obtained. Preferably to make the steel sufliciently age-hardening and to make the heat treatment economical a minimum of about 30% vanadium and carbon should be present. I

In order to be satisfactory as retaining rings in generators, the material must be capable of being hardened to a minimum of DPH hardness of 300. As will be noted from the examples given in Table I, this minimum DPH hardness of 300 DPH can be achieved by having about .40% carbon and 1.00/ 1.20% vanadium in the steel. However, vanadium is a very expensive element and, accordingly; other methods were sought to make this steel age-hardenable to the prescribed DPH hardness of 300. We have discovered that additions of aluminum to a steel containing nominally about carbon and .40% vanadium will produce steels that are capable of being aged to DPH hardnesses well in excess of 300.

The effects of aluminum on steels containing varying carbon and varying vanadium contents and also chromium and molybdenum are given in Table II and also shown on the graph of Figure 2.

We have also discovered that additions of about 4-5% chromium to our vanadium-carbon austenitic and thus nonmagnetic steels also will produce a steel that can consistently be age-hardened to a minimum DPH hardness of 230. See for example Table III and Figure 3.

Table III EFFECT OF CHROMIU'M IN A 0.40% C0.40% V STEEL Hardness (DPH) Steel No. C Mn N1 Cr V After Ag lng For 64 Hrs. at 1,200 F.

EFFECT OF CHROMIUM IN A' 0 40% o''0.75 1.0%' V STEEL This table further shows that with a 75% to 1.0% 059501- content, high chromium contents can be 055 1 7101- out seriously affecting the age-hardening properties.

The efiect of vanadium and carbon contentswith the preferred 4-5 chromium content are shown in Figures 4 .and 5 and tabulated inTables iv and v.

Table I1 EFFECT OF ALUMINUM Table IV Hardness 25 EFFECT OF CARBON IN A 5% Cr-1% v s TEEr Steel er 0 Mn N1 C-r A1 V Mo Aging For 64 Hardness Hrs. at (DPH)T 1,200 F. Steel No. 0 Mn N! Cr V Jitter Aglng'For 64'I-lrs .at 15.00 10.02 .02 1 172 1,200 E. 15.10 10.12 1.10 203 15.00 10.00 207 292 15.00 10.02 .48 430 .15 9.0 7.0 5.00 1.00,- 200 15. 25 9.51 3.07 320 .25 9.0 7.0 1 5.00 1.00- 350 14.80 9; 52 a. 04 355 .35 9.0 7.0 5.00 1.00 4 s73 10.05 9.98 2.90 345 .43 8.20 7.70 4.33 .89 30s 10. 04 9.90 3.10 410 .53 8 40 4.00 450 1. 07 410 10.47 9.99 2.84 1 s92 .58 8.20 4.80 4.52 1.02, 400 15.80 10.95 2. 94 359 .57 8.20 5.74 4.49 1.02 392 Hardness (DPH) T bl V a s For 116 a H a e t 2335 EFFECT OF VANADIUM IN .4 4.0 5.0%--or'-'-'.40%'o' STEEL 0 9-21 152' 2 2; "-5-,- 02 1 it??? .39 1s. 40 9.99 5.05 3.09 .28 .99 445 steelN 0 N1 or v fifg 64 Hrs. at

As will be noted, with an aluminum content above about 41 9. 8O 4. O2 3 98 53 327 3% .40% mimmum carbon content and a .40% m1n1mum 4 4, .1 00 25 213 vanadium content, the steel will consistently be capable 402 .44 7.40 3.91 479 .75 382 of being age hardened to a DPH hardness of well in excess 4 5,2 4,85 373 of 300. However, as shown in Figure 2, aluminum con- 3 58 9 g g: g 2%; tents between the residual amounts associated w1th suh- 4, 4 ,07 410 stantial deoxidation and about 1.2% have a harmful 313 effect on age-hardening. Accordingly, if used, this element should be present in amounts over about 1.2%. Increasing amounts thereof are beneficial so far as age- 1 hardening is concerned but other qualities of thesteel are seriously and adversely'afiected' if the aluminum exceeds about 4%.

Table VI EXAMPLEsoF THE STEELS HAVING HIGH Cr CONTENTS Hardness Steel No. Ni

Additions of up to molybdenum have been made to the steels of our invention, not only without harm to the aging reaction but withapparently a slightly beneficial eifejct. thereon. Amounts..over 4% may be; used-jprovided the austenite formers are adjusted within the ranges set forth above to offset the ferrite forming tendency of the molybdenum and maintain the steel in an austenitic condition. Under some circumstances, molybdenum may be desired for such purposes as increasing high temperature, strength, etc. The efiects of molybdenum are shown in the following Table VII:

Table VII EXAMPLES OF STEELS CONTAINING MOLYBDENUM Hardness (DPH) After Steel No. Mn N1 Cr V Mo Aging For 64 Hrs. at 1,200 F.

In all of the steels listed, it will be noted that the manganese-nickel contents vary over a considerably wide range, thus showing that the amounts of these elements are not critical insofar as age-hardening is concerned, but are present merely to make the structure of the steel austenitic.

As before stated, to age harden the steels of our invention, they are first solution annealed at a temperature sufficiently high to place the vanadium carbides in solu- Table VIII EFFECT OF SOLUTION ANNEALING TEMPERATURE Steel N o. 0 Mn Ni Cr V Hardness (DPH) After Aging For 8 Solution Annealing Temp. F.)

' Hours at 1,300 F.

The effects of aging temperatures following solution annealing at 2170 F. for 16 hour are shown inthe following Table IX. f

Table IX EFFECT-0F AGING TEMPERATURE or MATERIAL sono- TION ANNEALED AT 217o F. FOR ya HR. 1

Good results can "be obtainedby along time','64 hourtreatment at 1200" F. However, shorter times at higher temperatures up to about 1350 F. can be used. Other experiments have indicated that temperatures of at least 1100 F. must be used.

While we have shown and described a number of specific embodiments of our invention, it will be understood that these embodiments are merely for the purpose of illustration and description and that various other forms may be devised within the scope of our invention, as defined in the appended claims.

We claim:

1. Age-hardenable austenitic steel containing sufiicient metal from the group consisting of manganese, up to 12% nickel and a mixture thereof, to render the steel substantially wholly austenitic characterized by the absence of tungsten and containing in addition thereto about .25 to 1% carbon, about .30 to 3% vanadium, and about 1 to 4% molybdenum.

2. Age-hardenable austenitic steel containing sufficient metal from the group consisting of manganese, up to 12% nickel and a mixture thereof, to render the steel substantially' wholly austenitic characterized by the absence of tungsten and containing in addition thereto about .25 to 1% carbon, about .75 to 3% vanadium, 0 to 20% chromium and about 1 to 4% molybdenum.

3. Age-hardenable austenitic steel containing sufiicient metal from the, group consisting of manganese, up to 12% nickel and a mixture thereof to render the steel substantially wholly austenitic and containing in addition thereto about .25 to 1% carbon, about .30 to 3% vanadium and about 1.2 to 4% aluminum.

' 4. Age-hardenable austenitic steel containing sufficient metal from the group consisting of manganese, up to 12% nickel and a mixture thereof, to render the steel substantially wholly austenitic and containing in addition thereto about .40 to 1% carbon, about .40 to 3% vanadium and 3 to 4% aluminum.

5. Heat-treatment hardened austenitic steel articles containing sufi'lcient metal from the group consisting of manganese, up to 12% nickel and a mixture thereof to render the steel substantially wholly austenitic and in addition thereto between about .25 to 1% carbon, about .30 to 3.00% vanadium and about 1.2 to 4% aluminum, said steel being age-hardened by solution annealing at a sufliciently high temperature for a long enough time to place the vanadium carbides in solution and cooling followed by aging at a temperature between 1100 and 1500 F.

6. Heat-treatment hardened austenitic steel articles, DPH"hard'nes s" of 300 containing sufficient metal from the groupconsisting of manganese, up" w; 1 2% nickel and a mixture thereof to" render the steel substantially wholly austenitic and in addition thereto between about .40 to 1% carbon, about .40 to 3.00% vanadium and about 3 to 4% aluminum, said steel being age-hagdened @macgaaneanag at s'iifiiciently high temperature for sufficient time to place the vanadium carbides in sol ution and cooling followed by aging at a temperature between 1100 and 1500 F.

7. Heat-treatment harden ed austenitic steel articles containing sufficient metal from the group consisting of manganese, up to 12% nickel and a mixture thereof to render the steel substantially'wholly austenitic and in addition thereto between about .40. to 1% carbon, about .40 to 3.00% vanadium, 0' to 20% chromium, 0 to 4% molybdenum, about 1.2 'to"4% aluminum with the balance iro'nand elements in amounts which do not adversely a e pr perti aw id ,t .t=l i age-hardened by solution annealing for sufficient times at a sufiiciently high temperature and,coclirigjfollpwed by aging at a temperature between 1100 and 1500 F. I

8. Age-hardenable aiis'tenitic steel containing sufiicjient metal from the group consisting of manganese, up to 12% nickel and a mixture thereof to render the steel substantially wholly austenitic and containing in addition thereto about .25 to 1% carbon, about .30 to 3% vanadium, 0 to 20% chromium, 0 to 4% molybdenum and 1.2 to

4% aluminum.

9. Heat-treatment hardened austenitic steel articles containing sufficient metal from the group consisting of manganese, up to 12% nickel and a mixture thereof to render the steel substantially wholly austenitic and in addition thereto between about .25 to 1% carbon, about .30 to 3.00% vanadium, 0 to 20% chromium, 0 to, 4% molybdenum and 1.2 to 4% aluminum, said steel being hardened by solution annealing at a sufficiently high temperature for sufficient time to place the vanadium carbides in solution and cooling followed by aging at a temperature between 1100 and 1500 F.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AGE-HARDENABLE AUSTENITIC STEEL CONTAINING SUFFICIENT METAL FROM THE GROUP CONSISTING OF MANGANESE, UP TO 12% NICKEL AND A MIXTURE THEREOF, TO RENDER THE STEEL SUBSTANTIALLY WHOOLY AUSTENITIC CHARACTERIZED BY THE ABSENCE OF TUNGSTEN AND CONTAINING IN ADDITION THERETO ABOUT .25 TO 1% CARBON, ABOUT .30 TO 3% VANADIUM, AND ABOUT 1 TO 4% MOLYBDENUM. 